Transcript P2 summary: Designating habitable planets for follow

Satellite meeting - Designating habitable planets for
follow-up study: what are the relative parameter
spaces of RV and astrometry? (P2 Panel)
Scientific program
• Radial velocities to detect habitable planets in the visible:
performance and limitations (F. Pepe)
• Radial velocities to detect habitable planets in the nIR: performance
and limitations (E. Martin)
• Astrometry to detect habitable planets: performance and limitations
(M. Shao)
• Astrometry to detect habitable planets: future prospects (F. Malbet)
• Double blind tests (W. Traub)
Long-term precision
σO-C ~ 0.8 m/s rms (raw)
~ 0.3 m/s rms (time-binned)
P1 = 8.67 days M sini = 10.2 M
P2 = 31.6 days M sini = 11.8 M
P3 = 197 days M sini = 18.1 M
HD69830 - Lovis et al., Nature, 2006
F. Pepe
Error sources
Stellar noise (p modes,
activity)
Contaminants (Earth’s
atmosphere, moon, etc.)
Measurement noise
✴Photon noise
✴Instrumental errors (from
calibration to
measurement)
✴Calibration accuracy (any
technique)
F. Pepe
Beat the stellar limitations with
•
•
good targe selection
clever observational strategy
• Nearby cool stars are plentiful
• HZ planets have stronger RV signal
• Current NIR RV precision ~20 m/s
• New instruments & calibration methods need to be
developed to reach 1 m/s (CRIRES, CARMENES,
23/01/08
- Reunión Plan PRVS, SPIROU)
NAHUAL,
Estratégico
E. Martín 4
Impact of Star Spots on Astrometry and RV
Example:
Spot area 10-3, Sun @ 10pc
Astrometry
Spot bias
0.25 mas
Earth @1AU amp
0.3 mas
RV
1 m/s
0.09 m/s
• We find that for the Earth-Sun system, starspots
– do not appreciably interfere with astrometric detection.
– impose significant requirements on the number of
measurements and duration of an observing campaign needed
for radial velocity detection.
• Equiv ast noise ~0.08 mas  0.3 mas signature
• Equiv RV noise ~0.45 m/s  0.09 m/s signature
• Relative to a planet in a 1yr orbit, the star spot noise for
RV is ~10X larger than for Astrometry. (short periods
favor RV, long periods favor Astrometry)
M. Shao
F. Malbet
F. Malbet
10 pc sample
Henry 1998
Martín et al. 2004
E. Martín
Conclusions
Instrumental considerations:
• RV is a time-tested technique, although no proof
yet that it can get to a few cm/s (superEarths are
better)  but only minimum mass
• Prospects seem good (50 cm/s today)
• NIR RVs can help for planets in the HZs around
cool stars  ~10-20 m/s achieved so far but 1 m/s
needed
• Astrometry has 2D information and it is not
severely affected by inclination degeneracy
• Astrometry has not been tested at the mas level
(best performance 300 mas)
• Expensive space mission
Astrophysical noise
• Limitation to visible RVs since only inactive stars
(a few 10s within 15 pc) can be observed to the
highest accuracy
• This is less stringent for NIR RVs  ½ of the jitter
and more stars (Ms)
• Astrometry is less affected in solar-type stars
Final considerations
• Astrometry seems better suited to carry out a
census of habitable planets for follow up
• Especially so for Earth analogs (i.e., solar-like stars)
• RVs are more cost-efficient and can find some
valuable systems early on (JWST?)
• NIR RVs have good potential for nearby stars
F. Malbet